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Schematic cross-section through the sample, illustrating the plane of incidence, coordinate system, polar angle θ, pitch, λg, and the thickness of the layers. The patterned copper layer is etched from a single sided FR4 PCB laminate. These PCBs form the outermost layers of the sample, with the patterned copper layer facing inwards. For clarity, the 0.8 mm thick FR4 substrate is not shown.
Normal incidence (θ = 0), microwave electric field perpendicular to the slits, transmission data compared with FEM model predictions for the fundamental mode. The modelled data use the sample dimensions discussed previously and incorporates a small (10 μm-thick) air gap at the metal layer due to imperfections in sample design and limitations in assembly.
Predictions of the time-averaged electric (E) field on resonance (colour gradient) together with a schematic representation of the electric vector orientation at a phase corresponding to maximum field enhancement. Red regions correspond to field enhancements in excess of 10 times the incident field.
Predictions of the dependence of the peak transmission intensity of the fundamental mode on the aluminium film thickness, modelled using the Fourier modal method. 14 The complex permittivity of the aluminium has been set as . Inset: Optimisation of the resonantly transmitting system using the FEM model. Replacing the FR4 core with a low loss dielectric (dashed line) and then reducing the film thickness to 20 nm (solid line results in a transmission efficiency of 71%).
Experimental transmission measurements for p-polarised (TM) radiation in the region of the fundamental mode for −15° < θ < 15°.
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